1. Field of the Invention
This invention relates generally to microwave systems, and more particularly to a loaded line inverted microstrip phase shifter.
2. Description of the Prior Art
There are basically three alternatives for realizing phase shifters for use in airborne phased array antenna applications. The first alternative is the conventional microstrip approach which has been described in many technical articles e.g., "Integrated Diode Phased-Shifter Elements For An X-Band Phased Array", Mark E. Davis, IEEE Transactions on Microwave Theory and Techniques, December, 1975, pp. 1080-1084. Compared to this approach, the instant invention has much higher power handling capabilities and lower insertion loss. Furthermore, the inverted microstrip phase shifter has the advantage of being easy to hermetically seal.
A second alternative is the strip line approach described by F. G. Terrio et al, in the article entitled "A Low Cost Pin Diode Phase Shifter For Airborne Phased Array Antennas", IEEE Transactions on Microwave Theory and Techniques, June 1974, pp. 688-692. A phase shifter designed according to this approach would also have higher losses and lower power handling capability than one designed according to the instant invention.
The third alternative is a reciprocal ferrite phase shifter which has been described by C. R. Boyd, Jr. in his technical article entitled "A Dual-Mode, Latching Reciprocal Ferrite Phase Shifter", IEEE Transactions on Microwave Theory and Techniques, December, 1970, pp. 1119-1124. The advantages of the instant invention over ferrite phase shifters is its phase stability over a broad temperature range, and the fact that the required drivers and switching circuitry are much less complex for the instant invention. The two most important characteristics of microwave phase shifters in an avionic system are a high power handling capability and a low insertion loss. Total line losses in a microwave transmission line include dielectric losses and conduction losses for materials used in diode phase shifters. For this reason, the instant invention was conceived in order to reduce such conduction losses.
Accordingly, it is an object of the present invention to provide a microwave phase shifter that has a combination of characteristics which will enable it to overcome the aforementioned disadvantages of the prior art devices and which make it particularly well suited to the requirements of avionic equipment. In particular, the desired characteristics include a low insertion loss, a higher power handling capability, hermetic sealability, and small size.